Optical system for angular measuring instruments



E S iBPs m: CROSS REFERENCE T911 X? amaww 4 1357i I'M 1968 B. H. WELHAM 3,413 0 OPTICAL SYSTEM FOR ANGULAR MEASURING INSTRUMENTS Filed July 2, 1964 SCALE SURFACE RETICLE SURFACE BR/AN H WELHAM VENTOR United States OPTICAL SYSTEM FOR ANGULAR MEASURING INSTRUMENTS Brian H. Welham, Rochester, N.Y., assignor to Bausch & Lomb Incorporated, Rochester, N.Y., a corporation of New York Filed July 2, 1964, Ser. No. 379,991 1 Claim. (Cl. 350-202) ABSTRACT OF THE DISCLOSURE This invention relates to a novel optical system and more particularly to a unit magnification system which includes compensating means for use in angular measuring instruments or the like.

Angular measuring instruments of the type having circular-rulings and means sensing the positions of those rulings have recently been developed. The recently developed instruments have the potential to detect rotational movement of extremely small magnitudes. Such devices shoulddetect angular milliseconds when properly equipped with precision optical systems. For example, the devices which are disclosed and claimed in the copending application of Kreckel et al. SJN. 275,540 filed Apr. 25, 1963,.now abandoned, and assigned to the same assignee as the present invention are designed to detect and indicate minute rotational displacements. Accordingly, they have created a demand for aprecision optical system.

Measuring systems such as those disclosed in the aforementioned application include an imaging system for superimposing an image of a reticle and a scale, so that, an angular displacement of a portion of a cycle (a cycle being-one transparent and one opaque area) progressing from one reticle to another may be accurately measured. The imaging means for optical imaging areas of the scale or to image diiferent ones of the reticles onto different portions of the scale to thereby regulate the light intensity are utilized in those systems.

The optical systems disclosed and claimed herein represent an improvement on the systems called for in the copending application of J. Schwartz, entitled, Optical Systems}? Ser. No. 379,992 filed concurrently herewith, now Patent No. 3,370,903 and assigned to the same assignee as the present application. Both systems have been designedparticularly for the requirements of the angular measuring, instruments disclosed and claimed in the aforementioned Kreckel et al. application. The particular prob- 'lems relating to those devices have been overcome to a relatively high degree by the systems disclosed and claimed. herein. For example, thelens systems image each of eight" areas of a scale onto each of eight reticles at unit magnification. The spacings between the scale divisions are relatively small i.e. in the range of two seconds of arc interpolation to 100 seconds of are for a 500 millimeter diameter circular scale are obtainable with the present optical system.

Advantageousl-y, two sets of lines are imaged on each other by two objectives having collimated light between them in a manner which permits observation of the superposition. A beam splitter is so constructed and arranged that lateral movement of the beam splitter produces atent 3,418,037 Patented Dec. 24, 1968 minified displacement of the image of one set of lines with respect to the other to thereby provide means for accurately changing and/ or measuring any misalignment of the line sets.

Briefly, the present invention comprises an improvement in an optical system of the type having a pair of objectives placed back to back with their long conjugates at infinity. The separation of the objectives is such that they are separated by a distance equal to twice the exit pupil distance from the lens vertex nearest to the long conjugate. A beam splitter prism is inserted between the two objectives. Each of the objectives include the following axially aligned elements I through V. Elements I through V are numbered from the prism 11 rearwardly in objective 10 and elements I through V are the corresponding numbers in objective 10. The element I defines a double convex lens having the longer radius on the side of the prism. A second element II comprises a concavo- V convex lens element with the concave surface having a radius which matches the shorter radius of the element I and-is cemented thereto to form a compound lens. A

" fining surface being concave toward objective 10" and being disposed normal to the collimated beam so that lateral movement of the beam splitter in the direction of double headed arrow a will produce minified displacementof the image of one set of lines with respect to the other to thereby provide means for accurately changing and/or measuring the original misalignment of the line sets.

The lens systems according to the present invention will now be described in connection with the accompanying drawing, in which:

The single figure of the drawing is an axial section through a lens system according to the present invention. The lens system shown in the drawing comprises a-pair of objective lenses 10 and 10 and a beam splitter 11 separating the two objectives. The objectives are disposed in a back to back relationship with their long conjugates at infinity. Minimum aberrations were maintained in the systems by constructing each of the two objectives including the elements I through V and I through V respectively in accordance with the constructional data shown in Table A.

TABLE A 45.00 R R, 55.00 8.01 -R R 9.79 8.0l -R R 9.79 28.90 R R 35.32 13.32 R R 16.28

Ra, R3=0O 7.65 R R7 9.35 11.49 R R l4.05 11.49 R R l4.05 io, 1o= 3.55 t t 4.33 1.77 t t 2.l7 3.5l t t 4.29 3.39 t t 4.l5 3.67 t t 4.49 0.270 S S 0.330 0.576 S S 0.704 1.503 S S 1.837 2.394 S S 2.926

wherein R toR and R to R are the radii of the lens surfaces, t to it, and t to t are the axial thicknesses, and S to S and S to S are the axial spacings, the minus sign used with certain R designations denoting that such a lens surface is concave toward the beam splitter.

The two objectives are airspaced from each other by a distance of between 8.4 and 9.9 mm. A beam splitter of between 8.1 and 9.6 mm. is disposed between the objec-. tives.

It is also desirable to construct the lens system in acoordance with the constructional data set forth in Table B.

TABLE B wherein in to n are the indices of refraction and 1 to 11 are the Abbe numbers, of the elements I through V and 'I' through V' respectively.

The two objectives and 10' according to a preferred embodiment of the invention are separated by a distance of 9. 6 mm. and a beam splitter prism 11 which is 9 mm square and is disposed in the airspace which separates the objectives 10 and :10. The objectives according to the preferred embodiment conform to the following constructional data shown in Table C, the designations for the objective 10' being distinguished by a wherein R to R and R are the radii of the lens surfaces, t to t and if to are the axial thicknesses, S to S and S to S are the axial spacings, n1 to n are the indices of refraction and 11: to 11 are the Abbe numbers of the elements I through V for the objectives 10 and 10' and I through V' respectively.

The beam splitter 11 is preferably about 9 mm. square and within the range of 8:1 mm. to 9.9 mm. on each edge and has an index of refraction of between 1.5675 and 1.5775 man. One surface 12 of the prism 11 which is normal to the collimated light from a light source L, not shown, defines a slight power. The concave surface faces the adjacent objective and has a radii of between 1023 and 1251 mm. The preferred embodiment has a radius of curvature of 1137.6 mm; and an index of refraction of 1.5725.

While the invention has been described with respect to a specific application it should be understood that it may be modified or embodied in other forms without departing from the scope of the appended claim.

What is claimed is:

1. In an optical angular measurement instrument of the type having a pair of similar objectives disposed in a back to back relationship withtheir long conjugates at infinity and a single beam splitter cube disposed between said objectives, each of said objectives including five elements I through V respectively, a first element I defining a double convex lens having the longer radius on the side of the prism, a second element 11 comprising a concave convex lens having a radius equal to the adjacent radius of element I and in contact therewith, a piano convex singlet I-II airspaced from the element 11, and a doublet including elements IV and V airspaced from the singlet I-I-I, the doublet IV, V including a double convex lens IV having its shortest radius closest to the prism, the element V dcfining a plano concave lens, each of said elements I through V conforming substantially to the followingconstructional data:

TABLE 0 Element; Radius Thickness Index of Abbe or Spacing Refraction, m) Number, I:

R I R 00 81:3

1 1 1, 1' n, n=a94 n1=1.5180 v1=59.6

-e s a-3s 3 3 II, 11' 113124.97 1u=l.7200 vg=29.3

R I R 14 5 5 m, 111' a, a=a m=1.5390 61.2

Ru, Rs=Plano R I R 8 60 S S =L67 1 1= 1v, 1v n, n=a77 m=L5730 =5;

ii 151? 9 II: v,v' t5, t5=4.03 'n5=1 5760 v =41.4

Bio, Rio=Plano Element Radius Thickness Index of Abbe or Spacing Refraction, 1m Number,

S1, S1=.3 r B1", R1=50.OO I, I R i R 8 90 i1, t1=3.94 1A1=L518O i=59.6

a, a= R3', R3=8.90

11,11" a, z,=1.97 m=1.72o0 $29.3

R4 R 32.11 a SP0. 11]: 111' RFM'SO 2' as 3 !3= .-0 1L;=1.5890 1' =61=2 Rs, Rs=PIaI1O 9 3 S S =L67 I R7, R7=8.50 IV, IV R '7 R 12 77 i4, t4=3.77 m=1.5730 v4=57.4

9 a -Ra'i --R=12.77 V, V i t5=&.08 02 =L5750 vu=41.4

R10 Rro= Plano 6 the improvement comprising said beam splitter cube hav- References Cited ing a refractive surface defining a curvature of 1137.6 mm: UNITED STATES PATENTS in a plane normal to the axis of said objectives, and having 3,254,227 5/ 1966 Hock 350-247 an index of refraction of 1.5725, the cube being movable 5 JOHN K. CORBIN, Primary Examiner.

laterally of said axis to produce a displacement of the US (:1 X R image formed by said objectives 88-44; 350-214, 247 

